Steroids are highly immunosuppressive, particularly to T lymphocytes, and are frequently utilized in the treatment of autoimmune diseases to modulate immune responses. High doses of glucocorticoids can induce programmed cell death in immature T cells in the thymus as well as in a subset of peripheral T cells. However, the effects of steroids on the peripheral immune responses are not restricted to suppression. Intermediates in the steroid synthesis pathway can also influence the quantity and type of lymphokines produced by T cells upon activation. To date, the significance of the intimate relationship between steroids and the immune system is not understood. It has been hypothesized that at least in the thymus, steroids play a role in regulation of selection and tolerance. This role in regulation of the developing immune system is evidenced by a subset of antigen-presenting cells in the thymus capable of synthesizing glucocorticoids. Absence of these endogenously synthesized steroids during thymocyte development results in lack of development of thymocytes with a mature phenotype. Studies have been initiated to address the role that steroids may play regulating the peripheral immune response. Initial studies demonstrate the presence of cells in both spleen and lymph nodes capable of synthesizing pregnenolone, the first step in the steroid synthesis pathway characteristically found only in steroidogenic tissues. These cells are non-T, non-B cells which are ACTH-responsive, similar to that seen in the thymus. However, compared to levels detected in the thymus the peripheral tissues produce greater quantities of pregnenolone, both at basal levels and induced levels. Experiments will address whether this is due to an increased precursor frequency of steroidogenic cells, or actual increased synthesis. Future plans will include identification of the steroidogenic cells by cell surface phenotype analysis and immunohistochemistry, the characterization of the steroidogenic enzymes involved, by PCR and Northern blot analysis, analysis of the type of steroid synthesized and potential regulatory mechanisms that can control steroid production in the peripheral immune system. Ultimately, we will address whether these steroidogenic cells influence immune responses by analyzing splenic T cell proliferation and lymphokine production in the presence of steroid synthesis inhibitors.